While I've never fired the FN shotgun, I have manufactured several prototypes of an adapter that allows an AR15 collapsible stock to be mounted to a Remington 870 (see the Remington 870/AR15 Stock Adapter thread in the shotgun forum!). I've run over 500 rounds of slug and buckshot through the gun with the conversion, and can offer some insight to the handling characteristics of a shotgun with an AR style stock.